Device for use for mounting and alignment of a christmas tree on a wellhead

ABSTRACT

A mounting device for mounting a Christmas tree on a wellhead at sea, for use during a lowering of the Christmas tree from a platform to a drilling template which is located on the seabed. The mounting device includes an adaptor with end sections for connection with respective sections of the drilling template and the Christmas tree. The end sections of the adaptor have alignment bodies which are arranged for engagement with coacting alignment bodies of the drilling template and the Christmas tree.

BACKGROUND OF THE INVENTION

The invention concerns a device used for mounting and alignment of aChristmas tree which can be lowered from a platform to a wellhead whichis located on a seabed. The Christmas tree has a funnel which is wideneddownwardly, orientation bodies for angular positioning of the Christmastree relative to the wellhead, and connection bodies for connecting theChristmas tree to the wellhead. The device comprises a side element of adrilling template, which has a guiding device which is arranged toreceive a guide pipe, the guiding device comprises a conical funnel, andthe guide pipe is arranged to receive the wellhead and comprises acylindrical adaptor.

From the prior art it is known that when mounting a Christmas tree on awellhead, guidelines are employed which extend from the platform to thedrilling template, the guidelines being connected at the bottom to guideposts on to which sleeves of the Christmas tree are passed, and whichprovide a precise alignment of the Christmas tree in a horizontal planerelative to the drilling template.

The use of guide lines and a drilling template is described for instancein GB 2 285 274 which discloses a drilling template comprising a centralpart and arms that may be swung outwardly. Each of the arms is arrangedabove a well and a manifold is mounted at the central part. The well andthe manifold are interconnected through pipes.

Each well is completed by firstly introducing a drill string through anarm. and boring a hole into the formation underneath the arm. Thereaftera guide pipe or conductor is introduced into the hole and cemented therewhereby it is able to carry heavy equipment. The top of the guide pipeis welded to a guide pipe housing which comprises outer orientationelements such as pegs, which are adapted to be introduced intocorresponding slots in the arm. A guide base or plate is fixed to theguide pipe housing. During the lowering of the guide pipe/plate assemblythrough the opening in the arm the orientation elements are providing arotation of the assembly until its position is correct with respect tothe central part of the drilling template.

Guide posts wherefrom guide lines are running to a platform at the seasurface are provided at the base or plate.

The guide pipe housing is provided with internal steps in such a waythat it may support casings which are introduced into the well.

When a Christmas tree is to be mounted at the well, it is lowered andguided by means of the guide lines in such a way that the Christmas treeis oriented correctly with respect to the manifold at the central partof the drilling template. This is very important because the Christmastree and the manifold have pipe connector parts which shall beinterconnected during the lowering of the Christmas tree, and thetolerance with respect to the mutual angular orientation of theChristmas tree and the manifold is small.

The use of guide lines for drilling templates at very large depths isdifficult because the guide lines become tangled up. It is alsodifficult to keep the guide lines tensioned sufficiently.

In the case of drilling templates which are employed at very greatdepths where no guidelines extend therefrom to the platform, there aredifficulties involved in such an alignment.

SUMMARY OF THE INVENTION

The object of the invention is to provide a mounting device of the typementioned in the introduction which enables the above-mentionedalignment to be implemented.

The characteristics of the mounting device according to the inventionare presented in the characteristic features indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to thedrawing which schematically illustrates an embodiment of the mountingdevice according to the invention.

FIG. 1 is a perspective view of a component of a Christmas tree which ismounted on a wing element of a drilling template using the mountingdevice according to the invention, these components being separated fromone another.

FIG. 2 is a side view of a mounting device according to the invention,which is fitted in a receiving section of a wing element of a drillingtemplate, this section being cut through.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the drawing the direction indication “up” shouldhereinafter be understood as the direction towards the edge of thedrawing facing away from the reader.

As illustrated in FIG. 1 an adaptor 2 comprises an upper cylindricalpipe section 4 and a lower cylindrical pipe section 6 which areinterconnected via a conical pipe section 8 as is better illustrated inFIG. 2. The lower pipe section 6 is securely connected to the uppersection of a guide pipe 10 with an outer diameter of, e.g., 30″ (762 mm)which extends down into the well (not shown) and through a receivingsection 22 of a side or wing element 12 which is hinged to a centralsection of a drilling template (not shown).

An orientation or alignment of the adaptor 2 in relation to the sideelement 12 can be achieved by means of notches 14 which are provided inthe lower pipe section 6 of the adaptor 2, and which are arranged toreceive corresponding lugs 18 of a cylindrical section 16 of thereceiving section 22 of the side element 12. This engagement is achievedby means of a suitable rotation of the adaptor relative to the sideelement when they are brought into engagement during a lowering of theadaptor 2 from the platform and insertion of the adaptor 2 in thereceiving section 22. A conical funnel section 24 of the receivingsection 22 facilitates this insertion which is controlled by a remotelyoperated subsea vessel.

Through the guide pipe 10 there extends a casing 26 with an outerdiameter of, e.g., 20″ (508 mm), the top of which is securely connectedto a wellhead 28. This guide pipe is cemented to the casing 26.

In the upper pipe section 4 of the adaptor 2 there is provided at leastone lug or rib 32 which projects radially outwards.

A Christmas tree 40 has at the bottom a downwardly open entry funnel 42which is widened downwards, and which at the top changes into acylindrical tubular section (not shown) with an inner diameter which isslightly larger than the outer diameter of the upper pipe section 4 ofthe adaptor 2. This tubular section of the Christmas tree 40 is providedwith a downwardly open guide groove 30 which is adapted to the lug 32 ofthe adaptor.

When the Christmas tree 40 is lowered towards the wellhead 28 so thatthe wellhead 28 is first passed into the entry funnel 42 and then intothe tubular section of the Christmas tree 40, during which the lugs andthe guide grooves of the Christmas tree and the adaptor respectivelycome into engagement with each other, the object can be achieved thatthe Christmas tree and the adaptor are first aligned in such a mannerthat the tubular section of the Christmas tree 40 and the upper pipesection of the adaptor extend mutually coaxially, whereupon thesesections are aligned or oriented in relation to each other in ahorizontal plane and secured in the aligned position. By this meanscontact surfaces of the Christmas tree and the wellhead can finally comeinto engagement, thus giving support to the Christmas tree.

What is claimed is:
 1. A device for mounting and aligning a Christmastree (40) which can be lowered from a platform on a wellhead (28)located on a seabed, said device comprising: a side element (12)mountable on a drilling template; a guide pipe (10) arranged to receivethe wellhead, the side element (12) having a guiding device comprising aconical funnel (24) to receive the guide pipe; and a substantiallycylindrical adaptor (2), wherein the adaptor comprises a lower section(6) with alignment and orientation bodies (14) which are arranged tocoact with bodies (18) of the side element (12), a truncated cone-shapedintermediate section (8) which is adapted to the shape of the funnel(24) of the side element, and an upper section (4), which has an outerdiameter which is larger than the outer diameter of the lower section(6) and is adapted for insertion in a funnel (42) of the Christmas tree(40), and which has alignment and orientation bodies (32) adapted forcoacting with corresponding orientation bodies (30) of the Christmastree (40).
 2. A mounting device according to claim 1, characterized inthat the alignment bodies comprise lugs (18, 32) and notches (14, 30).